The formation of various integrated circuit (IC) structures on a wafer often relies on lithographic processes, sometimes referred to as photolithography, or simply lithography. As is well known, lithographic processes can be used to transfer a pattern of a photomask (also referred to herein as a mask or a reticle) to a wafer.
For instance, patterns can be formed from a photo resist layer disposed on the wafer by passing light energy through a photomask having an arrangement to image the desired pattern onto the photo resist layer. As a result, the pattern is transferred to the photo resist layer. Following a development cycle, the photoresist is selectively removed and the remaining resist serves to protect the underlying layer during further processing of the wafer (e.g., etching exposed portions of the underlying layer, implanting ions into the wafer, etc.). Thereafter, the remaining portions of the photo resist layer can be removed.
There is a pervasive trend in the art of IC fabrication to increase the density with which various structures are arranged. For example, feature size, line width, and the separation between features and lines are becoming increasingly smaller. For example, nodes with a critical dimension of about 45 nanometers (nm) to about 65 nm have been proposed. In these sub-micron processes, yield is affected by factors such as the quality of the patterned photo resist.
In situations where the photo resist is patterned to include a feature having a first dimension (e.g., a line width) that is small relative to a second dimension (e.g., a line length), the photo resist material comprising the feature can have a tendency to collapse. Collapsing can include completely falling over, leaning in one or more directions, bowing, “slumping,” or otherwise failing to remain upright and disposed in a desired direction. As should be appreciated, if a photo resist feature collapses, the underlying layer will not be processed as desired and performance of the resulting integrated circuit could be severely compromised. This problem is can become acute when the photo resist has a relatively large height (e.g., high aspect ratio), especially when the height is large relative to the first dimension.
FIG. 1 illustrates a conventional photo resist line 10 disposed on a wafer 12. In this example, the photo resist line 10 is used to define the size and location of a gate electrode structure for a transistor, such as a metal oxide field effect transistor (MOSFET). The photo resist line 10 has a first dimension D1 disposed in a first direction and a second dimension D2 disposed in a second direction. FIG. 2 shows the photo resist line 10 and wafer 12 in cross-section taken along the line 2—2 of FIG. 1. In the illustrated example, the wafer 12 can include a polysilicon layer 14 disposed under the photo resist line 10. The polysilicon layer 14 can be disposed over a dielectric layer 16 that, in turn, can be disposed over a semiconductor substrate 18. The illustrated photo resist line 10 can be used to protect the polysilicon layer 14 during formation of a polysilicon gate electrode from the polysilicon layer 14. In this example, the first dimension D1 would ultimately define a gate length and the second dimension D2 would ultimately define a gate width.
Although illustrated in an upright position, the photo resist line 10 exhibits properties that could lead to collapse of the photo resist line 10 (e.g., the first dimension D1 is relatively small compared to the second dimension D2 and/or a height of the photo resist line 10). At least one attempt has been made to reduce the occurrence of photo resist feature collapse. This attempt included using a spin-on bottom anti-reflective coating (BARC) under the photo resist material to add stability to the resulting photo resist features. Although the BARC layer may contribute desired optical qualities, this technique has not satisfactorily resulted in avoiding photo resist feature collapse.
Accordingly, there exists a need in the art for improved mircodevices and manufacturing techniques that have a reduced susceptibility to photo resist feature collapse.